The "I" in i-VTEC

[EuroAccord13]

Ok it means intelligent but I read in a mag somewhere that the new gen i-VTEC kicks in at any RPM as long as the ECU senses a change in throttle response in a sense that when it thinks more power is required, the VTEC kicks in... can someone confirm or deny this? If it's true.. it seems to break the whole powerband thing and I don't think I will like it.

[wynode]

LOL

It means it changes Cam timing.

i-VTEC engines have continuosly variable cam timing, but still only 2 stages of VTEC.

VTEC engines only DO NOT have continuosly variable Cam timing however.

Hence i-VTEC engines sense engine load and throttle position to adjust Cam timing, NOT when VTEC cuts in.

[Kit]

LOL

It means it changes Cam timing.

i-VTEC engines have continuosly variable cam timing, but still only 2 stages of VTEC.

VTEC engines only DO NOT have continuosly variable Cam timing however.

Hence i-VTEC engines sense engine load and throttle position to adjust Cam timing, NOT when VTEC cuts in.

Hey Wynode,

I'm not sure I understand this, I know how DOHC VTEC engines work.
But what do you mean by continuously varying the cam timing?
cos there is still only 2 sets of cam lobes on each cam right?

Did you mean Ignition timing?



Euro, it wouldnt make sense to cross over to VTEC (that is the second set of cam lobes) at lower RPM cos each cam lobe will have peak power at different parts of the rev range, hence VTEC engines have 2 cam lobes: one for tractability at low rpm, and the other for high rpm power.
If you did two dyno power runs one with the low rpm cam lobe only, and one with the high rpm cam lobe. The factory VTEC crossover point is where these two power curves overlap.

Doing standard bolt ons won't change the point at where these power curves overlap. So contrary to popular belief, installing a VTEC controller and bringing in the VTEC cutover point earlier on in the rev range won't give you more power, cos at that point, the high rpm cam lobe is producing less power than the low rpm cam lobe!

I hope that makes sense.
sorry to blabble on, its hard to explain it in a short paragraph hehehe

Chris

[wynode]

Kit,

Changing the cam timing is different to changing the valve lift.

Cam timing reffers to when the intake/exhaust valves open/close, not how much they open/close.

I suggest having a read of this

[wynode]

OK that article isn't the best, but the relevant part is this:

Some cars use a device that can advance the valve timing. This does not keep the valves open longer; instead, it opens them later and closes them later. This is done by rotating the camshaft ahead a few degrees. If the intake valves normally open at 10 degrees before top dead center (TDC) and close at 190 degrees after TDC, the total duration is 200 degrees. The opening and closing times can be shifted using a mechanism that rotates the cam ahead a little as it spins. So the valve might open at 10 degrees after TDC and close at 210 degrees after TDC. Closing the valve 20 degrees later is good, but it would be better to be able to increase the duration that the intake valve is open.

Think of it as having automatically (ECU adjusted) adjusted cam gears.

[McChook]

I honestly have never seen it written perfectly understandable. I know how it works in my head, but I doubt I could put it out in words, too much to remember, and what order do you put it all in....

That one however is one of the better descriptions

[wynode]

Just for the newcommers, i suggest you read the following:

Cam shaft operation Basics

Its the start of the link above. You really need to understand the basics to get an idea.

[Tofu]

yah....i-Vtec kicks ass..

[Kit]

OK that article isn't the best, but the relevant part is this:

Some cars use a device that can advance the valve timing. This does not keep the valves open longer; instead, it opens them later and closes them later. This is done by rotating the camshaft ahead a few degrees. If the intake valves normally open at 10 degrees before top dead center (TDC) and close at 190 degrees after TDC, the total duration is 200 degrees. The opening and closing times can be shifted using a mechanism that rotates the cam ahead a little as it spins. So the valve might open at 10 degrees after TDC and close at 210 degrees after TDC. Closing the valve 20 degrees later is good, but it would be better to be able to increase the duration that the intake valve is open.

Think of it as having automatically (ECU adjusted) adjusted cam gears.

hmmm just read that, so you were referring to the valve timing and not cam timing right?

cos i was wondering what you meant by cam timing.

Chris

[VTEC16]

when are you guys going to learn???


THERE IS NO "I" IN TEAM!

:twisted:

[w_civic]

hahahaha

[wynode]

hmmm just read that, so you were referring to the valve timing and not cam timing right?

cos i was wondering what you meant by cam timing.

Chris

Variable valve timing and variable cam timing mean the same thing. The cams operate the valves.

The keyword is valve timing as opposed to valve lift